Down-conversion mixer with signal processing

ABSTRACT

Systems and methods for implementing a down-conversion mixer with signal processing are disclosed.

BACKGROUND

In wireless communication systems, such as Ultra Wide Band (UWB),Wireless Local Area Network (WLAN), etc., a Radio Frequency (RF) signalundergoes processing and mixing with a local oscillator signal fordown-conversion of the RF signal into a baseband signal. In traditionalimplementations, down-conversion of the RF signal to the baseband signaltakes place in the current domain, however signal processing, such asamplification and filtering, takes place in the voltage domain. Inaddition, interfaces between signal processing blocks and mixing blocksare also in voltage domain in a classical RF receiver. Therefore,conversions of the baseband signal from voltage domain to current domainand vice versa usually take place several times. This can increasenoise, chip area and power consumption substantially.

Recently, more and more RF transceivers used in the wirelesscommunication systems have Very Large Scale Integration (VLSI) or evenSystem-on-Chip (SoC) level integration, and they support multi-bandand/or multi-standard operation. The signal processing blocks andmultiple RF frontend blocks including mixers are integrated in a VLSIIntegrated Circuit (IC). In most cases, multiple RF frontend blocksoccupy a large area, and the signal processing blocks may need to beappropriately separated from the RF frontend blocks for proper floorplanning. As a result, the signal processing block delivers a signal tothe RF block via long wirings. The passage of the signal via longwirings can couple noises to the interface nodes, and cause highconsumption of power for driving parasitic load of the long wirings.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numbersidentifies the figure in which the reference number first appears. Thesame numbers are used throughout the drawings to reference like featuresand components.

FIG. 1 are block diagrams illustrating an exemplary RF receiver sectionand a down-conversion mixer in a communication device.

FIG. 2 is a block diagram illustrating an exemplary RF receiver sectionof a communication device with a down-conversion mixer with signalprocessing capabilities.

FIG. 3 is a block diagram illustrating an exemplary high voltage versionof a down-conversion mixer with signal processing capabilities.

FIG. 4 is a circuit diagram of an exemplary high voltage version of adown-conversion mixer with signal processing capabilities.

FIG. 5 is a block diagram illustrating an exemplary low voltage versionof the proposed down-conversion mixer with signal processingcapabilities.

FIG. 6 is a circuit diagram illustrating an exemplary low voltageversion of the proposed down-conversion mixer with signal processingcapabilities.

FIG. 7 are circuit diagrams of exemplary current mode filters.

FIG. 8 is a flowchart of an exemplary method for implementing theproposed down-conversion mixer with signal processing capabilities.

DETAILED DESCRIPTION

Disclosed are techniques for implementing a down-conversion mixer withsignal processing capabilities. A down-conversion mixer with signalprocessing capability can be included in the RF receiver section ofcommunication devices, such as cellular telephones. The disclosedtechniques can also be used for both IC level design and printed circuitboard (PCB) level designs to reduce noise coupling, chip area, powerconsumption and the number of components employed in a circuit.

With the use of a Local Oscillator (LO) signal, the down-conversionmixer converts the received RF signal down into a baseband signal. Atfirst, the RF signal is down-converted into a baseband current signal,and the resulting current signal is then processed. The processing ofthe baseband signal includes amplification and filtering of the basebandsignal. The down-conversion mixer works on the principle of currentcommutating mixer (e.g., Gilbert mixer), combined with current domainsignal processing proposed. After signal processing, the basebandcurrent signal is converted to a corresponding baseband voltage signal.

The down-conversion mixer realizes each signal processing component onitself, saving chip area, lowering power consumption, and providing moreflexibility in floor planning. Furthermore, interface nodes betweendifferent components are in current domain, and are not as sensitive asthose in the voltage domain. Factors such as noise coupling andparasitic load effects from long wirings also have less influence on thecircuitry.

Exemplary Systems

The order in which blocks of systems in the following description ofexemplary block diagrams are described is not intended to be construedas a limitation, and any number of the described system blocks can becombined in any order to implement the systems, or alternate systems.Additionally, individual blocks may be deleted from the systems withoutdeparting from the spirit and scope of the subject matter describedherein. Furthermore, the systems can be implemented in any suitablehardware in IC level or PCB level without departing from the scope ofthe invention.

FIG. 1 illustrates a receiver section 100 of a communication device. TheRF receiver section 100 receives an RF signal 102. The RF receiversection 100 includes a down-conversion mixer 104 with a local oscillator(LO) signal 106, and signal processing blocks such as a filter 108 and aprogrammable gain amplifier 110. At the down-conversion mixer 104, theRF signal 102 is mixed with the LO signal 106, and the resultantbaseband signal is sent to the signal processing blocks for processing.After processing, a baseband voltage signal (VBB) 112 is obtained.

FIG. 1 further illustrates a typical down-conversion mixer 104. Thedown-conversion mixer 104 may be a current commutating mixer, such as aGilbert-cell mixer. The down-conversion mixer 104 includes a converter114 that converts the RF signal 102 into a current signal. The converter114 may include a transconductor. The RF current signal is thenconverted into a baseband signal in current domain. The conversion isperformed via a mixer 116, which receives the LO signal 106. The mixer116 may include a switching quad. The baseband current signal issubsequently converted into the VBB voltage signal 112 with the help ofa baseband load 118.

FIG. 2 illustrates a receiver section 200 of an exemplary wirelesscommunication device. The receiver section 200 receives the RF signal102 via an antenna 202. In one implementation, the RF signal 102 can becarrying audio, video, data stream, etc. For example, the RF signal 102can be received from any other communication device or a base station.The RF signal 102 in voltage is received by a Low Noise Amplifier (LNA)204.

The LNA 204 amplifies the RF signal 102, making the RF signal 102suitable for further processing. The LNA 204 provides a voltage gain.The LNA 204 can additionally provide electrical impedance transformationto the RF signal 102 before further processing. The RF signal 102 isthen fed to a mixer with signal processing capabilities 206, referred toas mixer 206, hereinafter.

The mixer 206 demodulates the RF signal 102 into a baseband signal. Inone implementation, the mixer 206 can be a down-conversion mixer withsignal processing capabilities. With use of the LO 106, the mixer 206converts the RF signal 102 into a baseband current signal, and thenprocess the baseband signal in current domain. The mixer 206 includesone or more current amplifiers and current-mode filters to amplify andfilter the baseband current signal. After amplifying and filtering, thebaseband current signal is converted to a baseband voltage signal by aprogrammable baseband load.

FIG. 3 illustrates an exemplary high voltage version of the mixer 206with signal processing capabilities. In the following description, thecomponents common with FIGS. 1 and 2 are referred to by the same namesand numerals.

The RF signal 102 received via the antenna 202 feeds a converter 114.The converter 114 converts the RF signal 102 into an RF current signal.The RF current signal is then fed to the mixer 116.

At the mixer 116, the RF current signal is mixed with the LO signal 106to generate a baseband signal in the current domain. The mixer 116receives the LO signal 106 and demodulates the RF current signal inaccordance with the LO signal 106. The LO signal 106 can be generated bya Local Oscillator (LO) generator or generation circuit (not shown). Themixer 116 can be implemented using cross-coupled differential pairs. Thebaseband current signal is then fed to a current-mode filter 300.

The current-mode filter 300 can be an electronic filter that filters acurrent signal to remove noise or any unwanted signals from the currentsignal. The current-mode filter 300 can be either an active filter or apassive filter. In one implementation, the current-mode filter 300 canbe implemented using an intrinsic second order filter from a regulatedcascode known in the art, which is further described below. The filteredbaseband current signal is then sent across a programmable baseband load302.

The programmable baseband load 302 converts the baseband current signalto the VBB signal 112. The programmable baseband load 302 can be eithera switched resistor array or a variable MOS resistor. The impedance ofthe programmable baseband load 302 can be varied to get the requiredconversion of the baseband current signal to the VBB signal 112.

FIG. 4 illustrates an exemplary circuit 400 for a high voltage versionof the mixer 206. The circuit diagram is intended to explain the conceptfor the high voltage version of the mixer 206 at an elementary level,and the number and type of electronic components depicted in the circuitdiagram does not limit the realization of the mixer 206. In thefollowing description, the components common to FIGS. 1, 2 and 3 havebeen referred to by the same names and numerals.

The circuit 400 for a high voltage version of the mixer 206 includeselectronic components such as transistors, current sources, resistors,voltage supply(ies), etc. In one implementation, for the high voltageversion, power supply voltage is able to support 4 or more stackedtransistors and/or resistors between power supply rails.

In the circuit 400, the transconductor is implemented via a differentialpair realized with the help of n-channel MOSFETs 404-9 and 404-10,referred to as nMOS 404-9 and 404-10 hereinafter, and a current source402-5. In an implementation, other type of transistors, such as bipolarjunction transistors (BJT), can also be used in place of the n-channelMOSFETs. The differential pair receives the RF signal 102 as input atthe gate terminals of the nMOS 404-9 and 404-10. The nMOS 404-9 receivesthe RF signal 102 with positive polarity, referred to as RF+ signal102-P, while the nMOS 404-10 receives the RF signal 102 with negativepolarity, referred to as RF− signal 102-N.

The differential pair converts the RF+ signal 102-P and the RF− signal102-N into corresponding current signals. The converted current signalsare then fed to the mixer 116.

The mixer 116 demodulates the RF current signals to a baseband currentsignal with the help of the LO signal 106. In one implementation, twocross-coupled differential pairs act as the mixer 116. The differentialpairs can be realized using n-channel MOSFETs 404-5 to 404-8. In analternate embodiment, other type of transistors, such as BJT, can alsobe used to realize a differential pair. The source terminals of the nMOS404-5 to 404-8 receive the current signals. The gate terminals to thenMOS 404-5 and 404-8 receive the LO signal 106 with positive polarity,referred to as LO+ signal 106-P, while the gate terminals to the nMOS404-6 and 404-7 receive the LO signal 106 with negative polarity,referred to as LO− signal 106-N.

The nMOS 404-5 to 404-8 form a multiplication function, multiplying thecurrent signals from nMOS 404-9 and 404-10 with the LO signal 106. ThenMOS pairs (i.e., 404-5 and 404-8, and 404-6 and 404-7) switch betweenthemselves to provide a baseband current signal with positive polarity,and a baseband current signal with negative polarity. The basebandcurrent signals are then fed as input to the current-mode filters.

The current-mode filters filter the current signals to remove noise orany unwanted signals. Active or passive current-mode filters known inthe art can be used for filtering the current signals. In animplementation, the current-mode filters can be implemented usingcurrent-mode bi-quad filters realized using n-channel MOSFETs 404-1 to404-4 and current sources 402-1 and 402-4 as shown. The current modefilters are explained in detail below. The filtered baseband currentsignals are then fed to the programmable baseband load 406.

In one implementation, the baseband load 406 can be either a switchedresistor array or a variable MOS resistor, although a fixed resistor orload may be implemented in simpler systems. At the baseband load 406,the baseband current signals are converted to the baseband voltagesignals, VBB 112-P and VBB 112-N.

The electronic components and the current sources in the circuit 400 aresupplied power via power supplies 408-1, 408-2, and 408-3, which can beobtained from a common source. In one implementation, the power supplycan be a DC supply derived from a battery or other DC source.

FIG. 5 illustrates an implementation of a low voltage version of themixer 206. In the following description, the components common withFIGS. 1, 2, and 3 have been referred to by the same names and numerals.

The RF signal 102, received from an input source, such as the antenna202, feeds the converter 114. The converter 114 converts the RF signal102 into a current signal. The current signal is then fed to mixer 116.

At the mixer 116, the current signal is mixed with the LO signal 106 togenerate a baseband current signal. The mixer 116 receives the LO signal106 and demodulates the current signal in accordance with the LO signal106. The LO signal 106 can be generated by a Local Oscillator (LO)generation circuit (not shown). The mixer 116 can be implemented usingtwo cross-coupled differential pairs. The baseband current signal isthen fed to one or more current amplifier(s) 502.

The current amplifier(s) 502 provides amplification to the currentsignal as needed. Switched current mirrors can be used for implementingthe current amplifier(s) 502. In an alternate embodiment,current-feedback operational amplifiers can be used as currentamplifier(s) 502. The amplified current signal can then be fed to thecurrent-mode filter 300.

The current-mode filter 300 can be an electronic filter that filters acurrent signal to remove noise or any unwanted signals from the currentsignal. The current-mode filter 300 can be either an active or a passivefilter. In one implementation, the current-mode filter can beimplemented using an intrinsic second order filter from a regulatedcascode, which is described below. Thereafter, the baseband currentsignal is sent across the programmable baseband load 302.

The programmable baseband load 302 converts the baseband current signalto the VBB signal 112. The programmable baseband load 302 can be eithera switchable resistor array or a variable MOS resistor, although a fixedresistor or load may be implemented in simpler systems. The programmablebaseband load 302 can be adjusted to obtain the required amplitude ofVBB signal 102.

FIG. 6 illustrates an exemplary circuit for a low voltage version of themixer 206. The circuit diagram is intended to explain the concept forthe low voltage version of the mixer 206 at an elementary level, and thenumber and type of electronic components depicted in the circuit diagramdoes not limit the realization of the mixer 206. In the followingdescription, the components common with FIGS. 1 to 5 are referred to bythe same names and numerals.

The circuit 600 for a low voltage version of the mixer 206 includeselectronic components such as transistors, current sources, resistors,voltage supply, etc. In an implementation, for the low voltage version,the power supply voltage is able to support maximum 3 stackedtransistors between the power supply rails.

In the circuit 600, the converter 114 that is implemented via a pseudodifferential pair realized with the help of n-channel MOSFETs 602-1 and602-2, referred to as nMOS 602-1 and 602-2 hereinafter. In animplementation, any other type of transistors, such as BJT, can also beused in place of the n-channel MOSFETs. The RF signal 102 is received asinput at the gate terminals of the nMOS 602-1 and 602-2. The nMOS 602-1receives the RF signal 102 with positive polarity, referred to as RF+signal 102-P, while the nMOS 602-2 receives the RF signal 102 with thenegative polarity, referred to as RF− signal 102-N.

The pseudo differential pair converts the RF+ signal 102-P and RF−signal 102-N into corresponding current signals. The current signalsobtained are then fed to a switching quad.

In one implementation, two cross-coupled differential pairs act as themixer 116. In an alternate embodiment, other type of transistors, suchas BJT, can also be used to realize a differential pair. The sourceterminals of nMOS 602-3 to 602-6 receive the current signals. The gateterminals to the nMOS 602-3 and 602-6 receive the LO signal 106 withpositive polarity, referred to as the LO+ signal 106-P, while the gateterminals to the nMOS 602-4 and 602-5 receive the LO signal 106 withnegative polarity, referred to as the LO− signal 106-N.

The nMOS 602-3 to 602-6 form a multiplication function, multiplying theRF signals with the LO signal 106. The nMOS pairs (i.e., 602-3 and602-6, and 602-4 and 602-5) switch between themselves to provide abaseband current signal with positive polarity, and a baseband currentsignal with negative polarity. Thus, the RF current signals aredemodulated to baseband current signals with the help of the localoscillator signal LO 106, and the baseband current signals are then sentto one or more current amplifier(s).

Current amplifier(s) 502 can be realized using switched current mirrorsor current-feedback operational amplifiers. In one implementation, thecurrent signal received from the nMOS 602-1 can be fed to a currentmirror realized with transistors pMOS 604-1 and 604-3. The currentsignal from the nMOS 602-2 can then be fed to a current mirror realizedwith transistors pMOS 604-2 and 604-4. The current mirrors amplify thebaseband current signals depending upon the mirror ratio of thetransistors pMOS 604-1 to 604-4. In an alternate embodiment, nMOScurrent mirrors can be used in place of pMOS current mirrors. Afteramplification, the current signals can be fed to the current-modefilters 300.

In an implementation, the current-mode filters 300 can be implementedusing current-mode bi-quad filters realized using n-channel MOSFETs602-7 to 602-10 and current sources 606-1 and 606-2. The current-modefilters 300 filter the current signals to remove noise or any unwantedsignals. Any active or passive current-mode filter known in the art canbe used for filtering the current signals. The current mode filters areexplained in detail later. The filtered baseband current signals arethen fed to the programmable baseband load 302 realized with the help avariable resistor 608.

The variable resistor 608 connected at the drain terminals of the nMOS602-8 and 602-9 can be adjusted to increase or decrease amplitude of theVBB signal 112. In an alternate embodiment, a variable MOSFET resistoror a switchable resistor array can be used in place of the variableresistor 608.

Referring back to FIG. 3, at the programmable baseband load 302, thebaseband current signals are converted to the baseband voltage signalsVBB 112-P and VBB 112-N. In one implementation, the programmablebaseband load 302 can be either a switched resistive or a variable MOSresistor.

Now referring back to FIG. 6, the electronic components and the currentsources in the circuit 600 are supplied power via a power supply voltage610. The power supply voltage 610 can be obtained from a DC supplyderived from a battery or any other DC source (not shown).

FIG. 7 illustrates an exemplary implementation of the current-modefilter. In one implementation, the current-mode filter 300 can beimplemented by a current-mode bi-quad filter 700. The current-modebi-quad filter 700 can be a second order low-pass filter. Thecurrent-mode bi-quad filter 700 can be realized using n-channelMOSFET(s) 702-1 and 702-2, referred to as nMOS 702-1 and 702-2hereinafter, and current sources 704-1 to 704-3. The transconductance ofnMOS 702-1 and 702-2 together with their gate to source capacitance areused as a second order filter current mode filter. The baseband currentsignal 706 can thereby be filtered in the current domain, thus producinga filtered signal 707.

The electronic components and the current sources in the circuit 700 aresupplied power via a power supply voltage 708. The power supply voltage706 can be a DC supply derived from a battery or other DC source.

FIG. 7 also shows another exemplary implementation of the current-modefilter 300. The current mode filter 300 can be implemented as a filter710. The filter 710 can be realized with the help of operationaltransconductance amplifiers (OTA) 712-1 and 712-2; capacitor(s) 714-1and 714-2; output resistances 716-1 and 716-2. The baseband currentsignal 706 can be filtered in a manner similar to that described abovewith reference to circuit 700, thus producing the filtered signal 707.

Exemplary Method

FIG. 8 illustrates an exemplary method for implementing adown-conversion mixer with signal processing capabilities. The order inwhich the method is described is not intended to be constructed as alimitation, and any number of the described method blocks can becombined in any order to implement the method, or alternate method.Additionally, individual blocks may be deleted from the method withoutdeparting from the spirit and scope of the subject matter describedherein.

At block 802, an RF voltage signal is received as an input fordown-conversion. In an implementation, the receive section of acommunication device, such as a cell phone, receives the RF signal 102.The RF signal 102 is processed and fed to the down-conversion mixer 206.Therefore, the RF signal 102 is down-converted to a baseband signal atthe mixer 206.

At block 804, the RF voltage signal is converted into a current signal.In one implementation, the RF signal 102 is converted into a currentsignal by the converter 114 included in the mixer 206.

At block 806, the RF signal is demodulated into a baseband signal, withthe use of a local oscillator (LO) signal. In one implementation, the RFcurrent signal is fed to the mixer 116. At the mixer 116, the RF currentsignal is mixed with the LO signal 106 to generate a baseband currentsignal. The mixer 116 receives the LO signal 106 and demodulates the RFcurrent signal in accordance with the LO signal 106. The LO signal 106can be generated by a Local Oscillator generation circuit. The mixer 116can be implemented using cross-coupled differential pairs.

At block 808, the baseband current signal is amplified and filtered. Inone implementation, the current signal can be amplified using one ormore current amplifiers. The current amplifier(s) 502 providesamplification to the current signal as required. Switched currentmirrors can be used for implementing the current amplifier(s) 502. In analternate embodiment, current-feedback operational amplifiers can beused as current amplifier(s) 502. The amplified current signal can thenbe fed to the current-mode filter 300.

The current-mode filter 300 can be an electronic filter that filters thecurrent signal to remove noise or any unwanted signals from the currentsignal. The current-mode filter 300 can be either an active filter or apassive filter. In one implementation, the current-mode filter can beimplemented using an intrinsic second order filter from a regulatedcascode.

The baseband current signal is sent across the programmable basebandload 302 where it is converted into the VBB signal 112.

CONCLUSION

Although embodiments for a down-conversion mixer with signal processinghave been described in language specific to structural features and/ormethods, it is to be understood that the appended claims are notnecessarily limited to the specific features or methods described.Rather, the specific features and methods are disclosed as exemplaryimplementations for the down-conversion mixer with signal processing.

1. A down-conversion mixer with signal processing capabilitiescomprising: a converter that converts a radio frequency (RF) signal intoa current signal; a mixer that receives the current signal, mixes thecurrent signal with a local oscillator signal, and generates a basebandsignal; a current-mode filter that receives the baseband signal, andgenerates a filtered signal; and a load that converts the filteredsignal into a baseband voltage signal.
 2. The down-conversion mixer ofclaim 1, wherein the converter is implemented as a differential paircomprised of MOSFETs.
 3. The down-conversion mixer of claim 1, whereinthe mixer includes two cross-coupled differential pairs using n-channelMOSFETs.
 4. The down-conversion mixer of claim 1, wherein the localoscillator signal is generated by a LO generation block.
 5. Thedown-conversion mixer of claim 1, wherein the current-mode filter is oneof an active or passive filter that removes noise and unwanted signalsfrom the current signal.
 6. The down-conversion mixer of claim 1,wherein the current-mode filter is a second order filter of a regulatedcascode.
 7. The down-conversion mixer of claim 1, wherein the basebandvoltage signal is obtained by programmable current amplifier orprogrammable baseband load.
 8. The down-conversion mixer of claim 7,wherein the programmable baseband load can be either a switched resistorarray or a variable MOS resistor.
 9. The down-conversion mixer of claim1 further comprising a current amplifier that amplifies the currentsignal.
 10. A device implementing down-conversion mixer with signalprocessing capabilities comprising: a Low Noise Amplifier (LNA) thatreceives and amplifies a radio frequency (RF) signal; and a mixer thatdemodulates the RF signal into a baseband signal comprised of: 1) aconverter that converts the RF signal into a current signal; 2) a firstcomponent that mixes the RF signal with a local oscillator signal; 3) asecond component that filters the baseband signal in current domain; and4) a third component that adjusts the amplitude of the baseband signaland outputs a voltage signal.
 11. The device of claim 10, wherein theconverter is implemented as a differential pair that includes a pair oftransistors.
 12. The device of claim 10, wherein the first component isa mixer that receives the current signal.
 13. The device of claim 12,wherein the mixer includes two cross- coupled differential pairtransistors.
 14. The device of claim 10, wherein the second component isa current-mode filter that receives the baseband signal, and generates afiltered signal.
 15. The device of claim 10, wherein the secondcomponent further includes a programmable current mirror that adjuststhe baseband signal.
 16. The device of claim 10, wherein the secondcomponent further includes a programmable baseband load that adjusts thebaseband signal.
 17. The device of claim 10, wherein the down-conversionmixer is further comprised of a current amplifier that amplifies thebaseband current signal.
 18. A method of down-converting a radiofrequency (RF) signal into a baseband signal with signal processingcomprising: receiving the RF signal for down-conversion; converting theRF signal from a voltage signal to a current signal; demodulating the RFsignal with the help of a local oscillator signal; generating thebaseband signal from the demodulation; filtering the baseband signal incurrent domain; and processing the baseband signal over a load.
 19. Themethod of claim 18, wherein the processing the baseband signal isperformed using a variable load.
 20. The method of claim 18 furthercomprising amplifying the baseband signal from the filtering.